In a common method of manufacturing laminated roofing shingles, a continuous mat such as a glass fiber mat is coated with asphalt and surfaced with granules, then cut longitudinally into overlay and underlay strips. The overlay strip is cut with a sawtooth pattern of tabs and cutouts. The underlay strip is positioned beneath the overlay strip, and the strips are joined together with adhesive to produce a continuous web of roofing material. The continuous web is cut laterally with an end cutter to produce separate laminated roofing shingles. In the manufacture of non-laminated roofing shingles, the shingles are cut with a plurality of tabs divided by slots.
The tabs, cutouts and slots are distinct portions of the roofing shingles that are distinguishable from adjacent portions of the shingles. The roofing shingles may also have other distinct portions, such as areas of the granules that are different in color or shading from adjacent areas.
When cutting roofing shingles, it is usually desirable to position the end cuts of the shingles at predetermined locations relative to the distinct portions. Such positioning is desirable for various reasons, including manufacturing predictability and improved aesthetic quality of the shingles. When the distinct portions are tabs, such positioning also avoids the formation of narrow end tabs that may tear away from the roofing shingles during manufacture or installation. U.S. Pat. No. 5,102,487 to Lamb discloses a method and apparatus for manufacturing laminated roofing shingles in which the end cutter is maintained in phase with the pattern of tabs on the web to control the positioning of the end cuts relative to the tabs.
To increase the productivity of the manufacturing operation, it would be advantageous to be able to simultaneously cut multiple stacked webs of roofing material with a single end cutter to produce multiple shingles at a time. However, the simultaneous cutting of multiple stacked webs of roofing material would greatly increase the difficulty in positioning the end cuts at predetermined locations relative to the distinct portions of the multiple webs. The Lamb patent does not disclose or suggest the simultaneous cutting of multiple stacked webs of roofing material. End cutters for cutting two stacked webs of roofing material are known, but the end cutters have not been used in a controlled method in which the end cuts are positioned at predetermined locations relative to the distinct portions of the webs. Therefore, it would be desirable to provide a method of controlled cutting of multiple stacked webs of roofing material to produce roofing shingles having end cuts positioned at predetermined locations relative to the distinct portions.